Postcranial anatomy and osteoderm histology of Riojasuchus tenuisceps and a phylogenetic update on Ornithosuchidae (Archosauria, Pseudosuchia)

VON BACZKO, M. BELÉN; DESOJO, JULIA B.; PONCE, DENIS

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Año: 2020 vol. 39

0272-4634

ABSTRACT?Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchian archosaurs from the Late Triassic ofSouth America and Europe. Riojasuchus tenuisceps is arguably one of the best representative species of this clade becauseit comprises very well-preserved three-dimensional, almost complete skeletons. However, R. tenuisceps was originallydescribed 50 years ago and compared then only with Ornithosuchus woodwardi and their affinities were discussed in detail.Here, we provide a detailed description of the postcranial skeleton of R. tenuisceps, which exhibits several remarkablefeatures within pseudosuchians. When a wide spectrum of pseudosuchian archosaurs are considered, the alleged characterthat linked ornithosuchids with dinosaurs resulted in convergences and some were registered in other pseudosuchiangroups as well. Riojasuchus tenuisceps also provided crucial information about the ?crocodile-reversed? tarsus, which is aunique feature of ornithosuchids, but it is not completely preserved in O. woodwardi and it is unknown in Venaticosuchusrusconii. In addition, the first histological analysis of cervical and dorsal osteoderms of R. tenuisceps was carried out as well,in order to test the utility of these structures as skeletochronological tools. Finally, the phylogenetic context ofOrnithosuchidae is discussed based on the latest phylogenetic studies, which show a close affinity with Erpetosuchidae